Heart disease and Alzheimer's are examples of diseases that involve electrically active cells, such as neurons and cardiomyocytes. Studying those cells is therefore important to helping people faced with such diseases.
One method of studying biological samples is fluorescence microscopy, a technique in which fluorophores are bound to the specimen to detect phenomena such as cell surface binding, neurotransmitter release, or specific DNA sequences. However, fluorophores and other compounds in the surrounding medium and even in the optical components of the microscope can autofluoresce and overwhelm fluorescence from the sample. Attempts have been made to reduce background fluorescence by using total internal reflection fluorescence (TIRF) microscopy. A TIRF microscope illuminates only a thin region of the sample so that fluorophores in the surrounding medium do not receive the excitation energy needed for fluorescence. However, existing TIRF microscopes require a prism to be pressed down onto the sample in a configuration that severely limits what conditions are allowable for the sample. For example, the TIRF prism occludes any culture media, as would be required for living cells, and prevents any physical access to the sample. Thus, fluorescence microscopy has not proven satisfactory for studying fine details of living, electrically active cells.